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Holiday calendar: A fractal puzzle, seen from space

Mike Hopkins / NASA

A Brazilian dam reservoir spreads out fractal fingers in a picture taken from the International Space Station.

NASA astronaut Mike Hopkins is puzzling over a picture that shows the jagged shoreline of a Brazilian dam reservoir, as seen from the International Space Station. His Twitter followers are puzzled as well: Where exactly is it?

"Interesting lake in Brazil with all the little fingers branching off," Hopkins tweeted on Tuesday. Those bizarre quasi-fractal shapes may add to the puzzlement by making it more difficult to pick out the pattern on a map. Jason Major, the space writer who blogs at "Lights in the Dark," suggests it's the Balbina Reservoir. Peter Caltner, a close observer of space station imagery, thinks it could be the Tucurui Reservoir. What's your guess? Feel free to share your sleuthing in the comment section. This puzzle picture is part of the Cosmic Log Space Advent Calendar, which features daily pictures of Earth from space through Christmas Day. For more tasty morsels, check out The Atlantic's Hubble Advent CalendarZooniverse's Advent calendar and the Galileo's Pendulum Science Advent Calendar.

Previously on the Space Advent Calendar:

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.